1. Field of the Invention
The present invention relates to an AF (auto focusing) control apparatus in which a plurality of movable lens groups serve as a focusing lens group during AF.
2. Description of the Related Art
The publication of Japanese Patent No. 2548307 discloses a zoom lens system having a plurality of lens groups. In this zoom lens system, only the rearmost lens group positioned closest to the image side operates as a focusing lens group. However, since the focusing sensitivity of the rearmost lens group is almost constant regardless of the focal length of the zoom lens system, the moving distance of the rearmost lens group during focusing is larger at the telephoto side than at the wide-angle side. Therefore, in such an AF mechanism, the AF operation at the telephoto side requires a large amount of time. Also, in order to shorten the minimum photographing distance as much as possible, a large moving distance of the rearmost lens group is required. However, the moving distance of the rearmost lens group cannot be sufficiently increased since interference with the lens group provided in front of the rearmost lens group must be avoided. Therefore, the minimum photographing distance cannot be shortened very much.
In this regard, an AF control apparatus has been developed in which two lens groups in a zoom lens system having a plurality of lens groups serve as a focusing lens. The two lens groups are moved together along an optical axis so as to reduce the moving distance of the two focusing lens groups during an AF operation and to shorten the AF operation time and the minimum photographing distance, particularly at the telephoto side (for example, Japanese Patent Laid-Open Publication No. Hei 7-120678).
However, if two focusing lens groups are employed as a movable lens group as disclosed in Japanese Patent Laid-Open Publication No. Hei 7-120678, a complex control system is required for controlling the operation of the focusing lens groups.